ok i have a 3.5L manual TF...

i noticed the other day on the way down the coast that when sitting on about 100km/h in 5th the car makes a thunder/rumbling sound(and not its not my exhaust rumble as its not done yet).there is a very little vibration in the seat,almost none through the steering wheel etc

but when i put it into 4th or 3rd and stay at the same speed on the highway the problem is non existant.also if i leave it in 5th and let the car roll on the highway at 10km'n there is no rumble/thunder..so to me that eliminates wheel balance..yeah?...

this problem doesnt exist on suburban streets when doing around 60km'h in 3rd or 4th gear...

what would it be...to me its along the lines of a busted mount but wouldn't i get this all gears?

any idea would be good

No idea, but some other things to try and narrow it down...

Have you tried cruising in other gears at the same RPM that produces the noise in 5th?

Also, if you were doing 90 in 5th then accelerate to and then past 100, does the noise suddenly appear at 100 and go away past that, or does it fade in and out, or change pitch?

Does a different road surface change the quality of the noise?

What direction does it sound like it's coming from? Front or back? left or right?

Have you checked you Cat??... I have just replaced mine on the 27th Dec, same similar sound, vibrated like a B!tch, anyways the guts of the cat was sh!thouse, replaced with new one, problem gone

3.5 litre in a TF ??

Didn't the 3.5 litre only come in Magnas as an option to the late model TH's and standard from the TJ on ?

I know the Verada's had it but they were KF's, not TF's and this car in question is a manual so it definately is not a Verada !!!

3.5 litre in a TF ??

Didn't the 3.5 litre only come in Magnas as an option to the late model TH's and standard from the TJ on ?

I know the Verada's had it but they were KF's, not TF's and this car in question is a manual so it definately is not a Verada !!!
yeah mine is a rare and hens teeth version...definately a TF and definately a 3.5Lmanual.

i will look at the cat soon as im getting a full exhaust system and i might "high flow" it..

No idea, but some other things to try and narrow it down...

Have you tried cruising in other gears at the same RPM that produces the noise in 5th?

Also, if you were doing 90 in 5th then accelerate to and then past 100, does the noise suddenly appear at 100 and go away past that, or does it fade in and out, or change pitch?

Does a different road surface change the quality of the noise?

What direction does it sound like it's coming from? Front or back? left or right?
yeah tried all that...didnt push the car past about 120 as i dont wanna get caught speeding.

up date on this...replaced engine mount as it was busted..thought yay i fount the prob...
took it for a spin and didnt fix it..

then took it to a work shop aand they sais the front left wheel bearing is gone..replaced that..
tocck it for a spin and didnt fit it.

the car has been in an accident before i got the car...

is it at all possible that the gear box could be out of line?or somethign is wrond with a drive shaft????or would i notice that happening all the time not just at hight speeds?

also with regards to the cat idea?what are the chances of that?mines only done135.000kms..however ill check that this weekend...how would i tell if thats rooted

If the gear box was even slightly out of line then you would no longer have a gear box.

In my mums VP an exhaust mount broke that caused a rumbling sound at about 90, or at hard acceleration, the same thing happened again when the weld on the cat broke.

At that sped you are probably hearing a harmonic resonance either from the driveline or the exhaust system.

Is the noise coming from the front? If so an idea would be to try the add on damper to go on top of the engine mount castings.

If the noise is coming from the rear it may be coming from the exhaust system mounts or from road / wheel vibration coming through the rear suspension.

Try at rest, in neutral. Gently push up the revs to the same speed that you have the noise. If you get someone els to be the driver you can work round the car to find the place where the noise is worst..

A good quick idea is to remove just one of the rear exhaust rubber hangers and try again. If the noise has gone then it is really a design issue as the mounting points are not quite in the correct place. Often replacing the mount rubbers with softer ones or ones where the exhaust side goes into a "Teardrop" that is formed inside the rubber ring will reduce the vibration.
If the exhaust is not the problem, I would look carefully at your suspension mounts, it may be the case that they need replacing.

Gerry

A mate of mine had a similar problem, albeit in a VT Commordore, which turned out to be injectors.

i agree with u guys..
i highly doubt it would be a gear box prob...she shift so smooth and quietly...and etc

i have a feeling it may be a suspension mount..

but i will also check for exhaust mounts....


today i could hear it making the sound on idle...opened the bonnet and it seemed to be commin the passenger side...around the area under the air box...

check to make sure that your tyres arent scalloped or worn abnormally usually makes a harmonic or resonating noise at higher speeds and is caused by wheel alignment or
faulty shockers

My TF did an output shaft bearing and I replaced the Lhs wheel bearing just for safes. Cannot for the life of me remember the noise it made, but do remember it was noticable in low gears. Sorry that isn't really helpful - just pointing out that the gearboxes do need love from time to time.

You need a co-pilot in the back seat to hang out the windows and listen for the noise

ok i have since replaced both wheel bearings from the front of the car.
had the tyres rotated,checked,balanced and alligned.
replaced gear box fluid and box had next to no filings in it.


i have also had the C.V's and engine mounts looked at they they said they were "fine"..i have doubts on how good they were chekced...

which only leaves the gearbox or drive shaft to be making a rumble..

a few people have said it may be a "loose hub" or bearing in the box..

what do u think

ok i have since replaced both wheel bearings from the front of the car.
had the tyres rotated,checked,balanced and alligned.
replaced gear box fluid and box had next to no filings in it.


i have also had the C.V's and engine mounts looked at they they said they were "fine"..i have doubts on how good they were chekced...

which only leaves the gearbox or drive shaft to be making a rumble..

a few people have said it may be a "loose hub" or bearing in the box..

what do u think
My $ is on the output shaft bearing given that there were 2x Magnas at the shop on the my car was in. All getting the same good news.